TITLE: GCN CIRCULAR NUMBER: 28722 SUBJECT: IceCube Alert 201021.28: Global MASTER-Net observations report DATE: 20/10/21 16:13:09 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, F.Balakin, V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, T.Pogrosheva, D.Kuvshinov, D. Cheryasov (Lomonosov Moscow State University, SAI, Physics Department), R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico Felix Aguilar OAFA), R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias), D. Buckley (South African Astronomical Observatory), O.A. Gres, N.M. Budnev, O.Ershova (Irkutsk State University, API), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), V. Yurkov, A. Gabovich, Yu. Sergienko (Blagoveschensk Educational State University) MASTER-Tavrida robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the IceCube Alert 201021.28 (trigger No 31008065,17h 22m 45.36s , +14d 39m 10.8s, R=0.51) errorbox 32837 sec after notice time and 32892 sec after trigger time at 2020-10-21 15:45:59 UT, with upper limit up to 17.5 mag. Observations started at twilight. The observations began at zenith distance = 45 deg. The sun altitude is -10.9 deg. The galactic latitude b = 26 deg., longitude l = 37 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1466141 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 32982 | 2020-10-21 15:45:59 | MASTER-Tavrida | (17h 20m 39.25s , +14d 38m 17.4s) | C | 180 | 16.7 | 33384 | 2020-10-21 15:52:41 | MASTER-Tavrida | (17h 20m 35.68s , +14d 38m 01.9s) | C | 180 | 17.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.